# B How would you find the magnetic force on a piece of metal by an electromagnet?

Does the metal being attracted make a difference?
How would you find the force on the metal knowing the field strength there?
How would you even calculate the field strength of an electromagnet with a core? In my case, it is one of those junkyard electromagnets.
thanks

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#### jrmichler

When you grab something with an electromagnet, you are making a magnetic circuit. To learn how to calculate, search magnetic circuit. The magnetic properties of the metal being attracted are part of the calculation. Keep in mind that the field strength is strongly affected by any air gaps, and that a layer of paint or rust is an air gap.

The force of attraction is proportional to the square of the field strength at the face of the electromagnet where it contacts the metal. A field strength of one Tesla has a pull force of 58 pounds per square inch of pole area.

#### hutchphd

The force of attraction is proportional to the square of the field strength at the face of the electromagnet where it contacts the metal. A field strength of one Tesla has a pull force of 58 pounds per square inch of pole area.
A useful number........there must be some assumption about the rest of the geometry, though? I am guessing this is for a "long" magnet with flat pole on a semi-infinite substrate??Any assumptions about substrate (obviously ferromagnetic I guess) but does it somehow not matter?I would find this a very useful thing to know but don't understand when to apply it. Thanks

yall i ended up just using FEMM and it worked out fine

"How would you find the magnetic force on a piece of metal by an electromagnet?"

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